In Electronic Toll Collection (ETC) systems, an on-board unit (OBU) transmits an indication signal indicating payment of a toll upon receipt of a wake-up signal from a road-side unit (RSU).
However, OBUs can have different signal reception sensitivities (also referred to wake up sensitivity) which can cause negative effects. For example, vehicles A and B are traveling one after another (e.g., B after A), an OBU installed on the vehicle B (referred to OBU B) is more sensitive than the one on the vehicle A (referred to OBU A). Therefore, the OBU B awakes and transmits a signal to the RSU indicating payment of a toll before than the OBU A, which causes a toll bar to rise to let vehicle A pass and then lower to bar vehicle B.
Accordingly, a method for calibrating OBUs and a method for ETC are therefore desirable.